In known audio and video communications terminals, the aiming direction of the camera is generally fixed. This means that in order to enable the subject to move to some extent in the field of the camera without the distant party losing the image of the subject, the viewing angle of the camera (as determined by the focal length of its objective lens) must be relatively large. This means that the screen of the distant videophone consequently reproduces an image in which the subject occupies a relatively small amount of space. In other words the subject is seen in a "long shot". This phenomenon is made worse by the fact that the screens of video telephones are generally small in size.
Simultaneously, studies have shown that users find a video telephone advantageous only if the distant party is seen in "close-up", i.e. with a smaller viewing angle and thus a longer focal length. This requirement therefore raises the difficulty that the slightest movement of the observed subject is likely to cause the subject to move out of the field of the camera, at least in part. In this respect, it may be observed that means for giving assistance in positioning, as described in U.S. Pat. No. 3,544,715, for example, turn out to be unusable in practice since they require too high an effort of concentration on the part of the user. More precisely, although these devices are capable of operating satisfactorily technically speaking, they are unsatisfactory ergonomically speaking.
Thus, the state of the art teaches no practical solution enabling a distant party to be observed in close-up while still allowing that party to move relatively freely relative to the terminal. Simultaneously, it appears that these two contradictory requirements are going to be fundamental if the video telephone is to be a success on a large scale.
The present invention therefore seeks to remedy the limitations of the proir art by providing a video telephone type of terminal in which the distant party can be observed in close-up without requiring that party to occupy an extremely fixed position in front of the camera in his or her own terminal.
More generally, the object of the present invention is to provide a terminal in which the party using the terminal is not subjected without any possibility of intervention, to comfort-reducing degradation in the quality of the image (and optionally sound) information received by that terminal.